1. Field of the Invention
This invention relates to a process for enhancing the solution diffusibility of a developing liquid in a semiconductor wafer developing unit.
2. Description of the Prior Art
The current practice is to develop a photoresist on the surface of a substrate while the substrate is rotating on a wafer chuck. This mechanical rotation is essentially static, as far as the developer is concerned, and developing speed is limited by solution diffusibility. This is because the developer becomes stagnant with photoresist and fresh developing liquid cannot diffuse toward the photoresist. As a result, development ceases.
While integration density is steadily increasing, the art of improving methods of developing photoresist has lagged behind with respect to increased solution diffusibility, developing speed, or feature uniformity.
A variety of methods have been described in the patent literature dealing with irradiation of photoresist, depositing of photoresist, or applying of spin-on-glass. But there appear to be no prior art teachings regarding methods of enhancing developers, be they organic solvents for negative resists or alkaline solutions for positive resists. U.S. Pat. No. 4,612,267 (Heitmann et al.) discusses the ultrasonic irradiation of a resist layer. U.S. Pat. No. 5,395,803 (Adams) discloses a method of depositing a material, such as a photoresist, upon a substrate. U.S. Pat. No. 5,454,871 (Liaw et al.) describes an apparatus for applying spin-on-glass material to a wafer under controlled humidity conditions.